The present invention is generally directed to photoplethysmographic measurement instruments, and more specifically to clip-type pulse oximetry sensors which attach to patient appendages.
A common technique used to monitor blood oxygen levels is pulse oximetry. In this regard, it is known that the light transmissivity and color of blood is a function of the oxygen saturation of the heme in the blood""s hemoglobin. For example, heme that is saturated with oxygen appears bright red because saturated heme is relatively permeable to red light. In contrast, heme that is deoxygenated appears dark and bluish as it is less permeable to red light. A pulse oximeter system measures the oxygen content of arterial blood by first illuminating the blood with red and infrared radiation and determining the corresponding amounts of red and infrared radiation that are absorbed by the heme in the blood. In turn, such light absorption amounts may be employed in conjunction with known calibration information to determine blood oxygen levels.
Pulse oximetry sensors generally include one or more light emitters, a detector, and a means for holding the emitter(s) and detector in contact with a patient""s tissue so that an optical path is established through the tissue. There are various means for holding the emitter(s)/detector in contact to a patient""s tissue; however, two common types are flexible and clip-type sensors. Flexible sensors may simply comprise an adhesive strip onto which the emitter(s)/detector are mounted for placement about a patient appendage. Clip-type sensors typically include two hingedly connected housings onto which the emitter(s) and detector are mounted. Generally, clip-type sensors are releasably attached to a patient""s appendage (e.g., finger, ear lobe or the nasal septum) so that the appendage is isolated between the two housings.
Both mentioned sensor types present advantages and disadvantages. In particular, clip-type sensors may be advantageously reused on different patients and are relatively easy to attach to and remove from a patient tissue site. Further, the present inventor has recognized the desirability of providing a reusable sensor which securely attaches to a patient""s appendage while reducing any interference with blood circulation, which is resistant to contamination, which yields reduced relative appendage movement, which is durable and which is configured for ease of assembly.
In view of the foregoing, a primary object of the present invention is to provide a reusable oximeter sensor which securely and reliably attaches to a patient""s appendage while reducing any arterial blood flow interference.
Another objective of the present invention is to provide a reusable oximeter sensor that inhibits contaminant infiltration.
A further object of the present invention is to provide a reusable oximeter sensor which reduces relative movement of an inserted appendage.
An additional object of the present invention is to provide a reusable oximeter sensor having enhanced durability.
Yet another objective of the present invention is to provide a reusable pulse oximetry sensor which is relatively easy to assemble.
One or more of the above objectives and additional advantages are realized by the present invention. In one aspect, a clip-type pulse oximetry sensor is provided which comprises top and bottom members disposed in opposing and hinged relation, and a spring member interposed therebetween. More particularly, a resilient spring member may be located between the sensor""s top and bottom members near a rearward end of the members (e.g., an end opposite to that which securably receives a patient appendage). The resilient spring member acts to provide the force required to close and thereby hold the forward ends of the top and bottom members on a patient""s inserted appendage. Of note, the closing force may be provided by a combination of tensile and compressive portions integrated into the spring member. That is, when the sensor is secured upon a patient appendage a portion of the resilient hinge member is actuated to be tensioned and another portion is actuated to be compressed. Attempting to return to their non-deformed static condition, the tensile and compressive portions combinatively exert an enhanced closing force to reliably hold the sensor to the inserted appendage.
Preferably, contact surfaces of the spring member directly engage both the top and bottom members when the sensor is assembled, thereby facilitating force transfer therebetween. The contact surfaces may comprise wings which extend rearwardly at the top and bottom of the spring member. Relatedly, rearward ends of the top and bottom members may be rimmed and/or otherwise configured to provide conformal seats for flushly receiving the spring member wings. When compressive forces are applied to the rearward ends of the top and bottom members (e.g., via hand manipulation) the spring member wings are forced towards one another, compressing a rearward-facing portion of the spring member while tensioning a forward-facing portion of the spring member. Correspondingly, the forward ends of the top and bottom members will open to accommodate patient appendage insertion/positioning therebetween. When the compressive forces are released, the tensile and compressive portions of the spring member co-act to provide the above-noted closing force.
A rearward-facing side of the spring member (e.g., extending between the above-noted wings) is preferably defined by a continuous surface. For example, in a winged embodiment having a U-shaped profile, the rearward side of the spring member may comprise a concave, semi-cylindrical surface that extends between the top and bottom members across the width of the sensor to completely close the rear-end of the sensor. As may be appreciated, the provision of a continuous rearward surface on the spring member reduces contaminate infiltration into the sensor.
Of note, the spring member may be advantageously defined as a one-piece unit. More particularly, the resilient spring member may have an integral, monolithic structure. To provide such a structure, the spring member may advantageously comprise a molded polymeric material.
In the latter regard, and more generally, the resilient spring member preferably comprises an elastomeric material. By way of example only, the spring member may a material selected from a group consisting of thermoplastic elastomers, liquid silicone rubbers, polyolefin elastomers, thermoplastic rubbers urethanes and natural rubbers. The utilization of an elastomeric spring member facilitates the realization of a range of spring constants for different applications of the inventive sensor. As such, the same basic design/componentry of the inventive sensor may be employed for a number of different patient applications entailing different desired clamping forces for patient appendage securement. That is, only the specific elastomer utilized in the spring members needs to vary from sensor to sensor. For example, a large-finger patient sensor may comprise a spring member having a different modulus of elasticity than that of another spring member utilized in a small finger patient sensor.
Preferably, the spring member may comprise one or more openings to accommodate hinged interconnection of the top and bottom members and/or to allow for the routing of electrical wiring between the top and bottom members. More particularly, the spring member may comprise an opening extending laterally therethrough from side to side to accommodate a hinge pin that hingedly interconnects the top and bottom members. In this embodiment, the hinge pin acts as a fulcrum or hinge axis for the top and bottom members. Additionally, the hinge pin functionally separates the above-noted tensile and compressive portions of the hinge member. For example, when the sensor is opened (e.g. to accommodate insertion or after insertion of a patient appendage), the portion of the spring member in front of the hinge pin is pulled in tension while the portion rearward the pin is compressed.
The spring member may also include a slot that extends from the top of the spring member to the bottom thereof to provide a passageway to route electrical wiring for emitter and/or detector componentry carried by the top and bottom members. Preferably, the slot is located on a forward-facing side of the spring member. In one embodiment, the slot is located on the spring member""s vertical centerline and extends from the front of the spring member and in to the lateral opening of the spring member. This arrangement effectively divides the above-noted tensile portion into two separated sides. During assembly electrical wiring for emitter and/or detector componentry may be routed through the slot and retained behind the hinge pin, thereby isolating and protecting the wires.
The lateral opening through the resilient spring member may also advantageously include a keyway slot. Correspondingly, the hinge pin may include an outwardly projecting key member slidably positionable in the keyway slot. Such an arrangement orients the hinge pin about a symmetry plane of the spring member. During actuation of the spring member, the slot allows the hinge pin to float with the symmetry plane, thereby equalizing the stress within the spring member. In turn, the actuation life of the spring member may be enhanced.
According to another aspect of the present invention, a clip-type pulse oximeter sensor is disclosed that comprises opposing and hingedly connected top and bottom members, and a cushion interconnected to one of the top and bottom members. Preferably, cushions are interconnected to each of the top and bottom members.
Each cushion may comprise a frame and a pliable member supported about a polygonal area by the frame. In turn, an optical window (e.g., a plastic lens) may be supported about its periphery within said polygonal area by the pliable member. Generally, each cushion may be interconnected to a top or bottom member, wherein the pliable member is free to flexibly conform to a patient""s appendage and thereby locate the optical window in intimate relation to the patient appendage. Relatedly, one or more light emitter(s) or light detector(s) may be located adjacent to, and preferably connected to, each optical window.
Of note, the pliable member may comprise an elastomeric material (e.g., a synthetic rubber) that is over-molded onto the frame. In turn, the frame may comprise a molded polymeric material (e.g., a glass-filled polymer that bonds well with an elastomeric pliable member). Such an arrangement enhances the pliable member/frame interconnection and facilitates effective load transfer therebetween.
Of note, the cushions may be advantageously attached to the top and bottom members using snap-fit means. The snap-fit means may include a plurality of interconnecting member sets to attach each given cushion to a top or bottom member. Each of the interconnecting member sets may comprise a projection and a mating recess. In turn, each of the cushions and top and bottom members may comprise at least one projection and at least one mating recess to facilitate secured interconnection therebetween. Further, the recesses may be configured so as to restrict movement of a corresponding projection in at least two dimensions.
As may be appreciated, the projections and recesses may be integrated into the above-noted cushion frames and interfacing top and bottom members. In such arrangements, the frames and each of the top and bottom members may advantageously comprise at least one projection and at least one mating recess. Preferably, different ones of a plurality of interconnecting member sets may be located on the opposing sides of the sensor and on the forward side of the sensor.
As noted, a plurality interconnecting member sets may be advantageously utilized. Preferably, these interconnecting member sets are oriented so that their respective interconnection axes are transverse to one another. By transversely orienting the connection axes, a given cushion may be securely locked into a top/bottom member to restrict relative movement in three dimensions. For example, use of interconnecting members sets on at least two sides of a polygonal (e.g. rectangular) cushion frame and interfacing bottom/top member facilitates a secure interconnection both laterally and longitudinally, as well as in the depth profile. Such arrangements effectively restrict relative movement between sensor componentry upon patient movements during use.
Additional aspects advantages of the present invention will become apparent upon consideration of the further description that follows.